New-Guinea has been called by A. R. Wallace the greatest terra incognita that still remains for the naturalist to explore, and the only region where altogether new and unimagined forms of life may perhaps be found. This he wrote in 1869 and we now living in 1906 can, as a matter of fact, underline this sentence, for, notwithstanding the number of new forms has amazingly increased during the latest years of the 19th century, this largest of all islands remains still a terra incognita, as all the explorers have collected merely in a few localities here and there along the coasts, the interior of this enormous island remains a gigantic white patch on the map; we do not undervalue Dr. A. B. Meyer’s crossing the island from the Geelvink-bay southwards, nor the english exploration of the Fly-river a. s. O., but a look at the map — and we still must confess that, relatively spoken, nearly nothing has been done to decrease the terra incognita. We are convinced however that the way to the interior of the large island is entangled with all kinds of difficulties, nay that it generally is not without peril of life to live some time on the coast, and we therefore appreciate every endeavor to explore that most interesting island. The explorations of the latest 25 years have enriched our knowledge of the New-Guinea Mammals really in an unexpected way. Dr. O. Finsch (Neu-Guinea und seine Bewohner, 1865) enumerated a number of 15 mammals from New-Guinea: 2 bats, 10 marsupials, 1 pig, 1 cetacean, besides Paradoxurus hermaphroditus. Wallace wrote in 1869 (the Malay-Archipelago, Vol. II, p. 428): “the mammalia of New-Guinea and the adjacent islands yet discovered, are only seventeen in number; two of these are bats, one is a pig of a peculiar species (Sus papuensis), and the rest are all marsupials”. A. Milne Edwards said in 1877 (Compt. rend. p. 1081): “l’ordre des Rongeurs est représenté à la Nouvelle Guinée par sept espèces”. In 1878, von Rosenberg registered 20 mammals from N. G. (Der malayische Archipel, p. 549), meanwhile K. M. Heller could give a list of 70 mammals inhabiting New-Guinea, Yule-island, Mysore and Jobie (Abhandl. Dresden Museum, 1896/97, Bd. VI, No. 8). Dr. H. D. Tjeenk Willink (De Zoogdieren voorkomende in Nederlandsch Indie, 1906) enumerated 62 mammals, mostly from Dutch New-Guinea. I could point out that up to this year (1906) nearly the double number has been described! In order to clean the path to future investigators, I have undertaken the difficult task to study all what hitherto has been written concerning the mammals of New-Guinea, so that I exhibit in the following pages a rather complete list of them, together with short descriptions if convenient, with measurements where I judge it necessary, and mostly with a compilation of where a species has been described, with author, locality a. s. o. To my great surprise I found that there have been described from New-Guinea about 40 Bats, about 40 Mice, about 50 Marsupials and Monotremes and 2 Pigs: in all 126 mammals! I think this may be called a rather respectable number, the more as New-Guiuea always passes for very poor in mammals! In my view it is somewhat premature to speak of “poor” or “abundant” unless having any notion of what is living on the mountains and in the interior of an island greater than Borneo, of the double size of Great Britain! The unexpected mammalian fauna found in the mountainous interior of the Philippines, may be a warning against useless and premature judgements and conclusions!